The present invention relates to appliances in general, and more particularly to improvements in appliances of the type wherein a mobile tool can be shielded by a guard to reduce the likelihood of injury to the operator. Typical examples of such appliances are household slicing machines for bread or other foodstuffs wherein a rotary disc-shaped severing tool is normally installed in a vertical plane and the housing of the machine confines an electric motor which can be started to rotate the tool.
German Utility Model No. 7 611 681 (corresponding to U.S. Pat. No. 4,070,941) discloses a household slicing machine with a protective guard or shroud which is detachable from the housing of the machine and permits the actuating means for the motor switch to start the motor only when the guard is properly attached to the housing. The actuating means comprises a trip for the switch, and such trip is reciprocably mounted in the upper part of the housing of the slicing machine. A barrier is shiftable at a level below the lower end of the trip to oppose the depression of the trip and closing of the motor switch when it extends into the path of downward movement of the trip. A spring is provided to urge the barrier toward the front wall of the housing and into the path of downward movement of the trip. The guard or shroud of the machine which is disclosed in the Utility Model is designed to overlie portions of the rotary disc-shaped slicing knife and has lugs and holding fingers which can be inserted through openings provided therefor in the housing of the slicing machine. One such opening is located in the region of the barrier so that, when the guard is properly affixed to the housing, a selected one of its holding fingers moves the barrier away from the path of downward movement of the trip and the latter can be depressed in order to complete the circuit of the motor which begins to drive the slicing knife. The selected holding finger of the guard then overcomes the bias of the spring which urges the barrier to its blocking position, i.e., into the path of movement of the trip in a direction to close the associated switch and to thus complete the circuit of the motor.
The just described appliance exhibits the advantage that the motor cannot be started as long as the guard is not properly affixed to the housing. The aforementioned spring ensures that the barrier reassumes its blocking position in immediate response to separation of the guard from the housing. However, the just described appliance also exhibits certain drawbacks. For example, the guard cannot completely conceal (i.e., prevent access to) the slicing knife when it is properly affixed to the housing. Thus, the motor for the slicing knife can be started as soon and as long as the guard is properly attached to the housing. This can lead to injuries if the motor is started accidentally when the appliance is not intended to be used. Moreover, it is not possible to shield the slicing knife from contamination when the guard is properly applied but the appliance is not in use for extended periods of time.
The aforementioned copending application Ser. No. 665,128 of Norbert Flammann for "Household appliance with an adjustable guard for a rotary tool" discloses an improved slicing machine wherein the guard is not only separable from the housing but is also shiftable relative thereto in a plane which is preferably parallel to the plane of the slicing knife. Moreover, the appliance of Flammann embodies a blocking device which prevents closing of the starter switch for the motor which drives the slicing knife when the guard is detached, when the guard is barely attached or when the guard prevents access to the knife. This enhances the safety of the appliance because the operator can readily manipulate the guard and/or other parts of the appliance whenever the guard is detached as well as when the guard is attached but is not held in a position in which it exposes a portion of the slicing knife so that the latter can be put to actual use. The appliance of Flammann exhibits the additional advantage that the guard can completely conceal the knife, at least from the front side of the housing, to thus positively prevent injury to a careless or immature manipulator as well as to shield the knife from unnecessary contamination during long periods of non-use while the guard remains attached to the housing. In order to shift the guard from one position to another position, it is merely necessary to engage and push or pull a suitable handgrip which is preferably integral with the guard. This constitutes a convenience because the guard can be shifted to any selected position with the exertion of a relatively small force. However, such ready shiftability of the guard also represents a potential danger, e.g., to a child, if the operator shifts the guard to a position for use of the appliance in which the trip for the motor switch can be readily depressed to start the motor which drives the knife. On the other hand, such mounting of the guard that it can be shifted only in response to the exertion of a pronounced force which would prevent children from changing the position of the guard is also undesirable because this would present problems to a housewife by rendering the manipulation of the guard too cumbersome and strenuous.